1 answer

1 Is there a way to know what are the hosts contained in a cell using API?
currently i dont think, but in v2 there is a new DB nova_api which have host mapping to cell table

2 Are cell contained in a region or is a concept cross different region;
In Region you have all openstack components in one region and common Horizon and/or keystone
Cell is for scaling the NOVA, for each cell have its own DB and AMQP and API only at API cell

4 Can cell be sub partitioned in host aggregate and in case an host aggregate have to be fully contained in cell?
it is not supported officially, but yeah there are few deployments where cells have Availability zones and host aggregates